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Answer:
2 4/7 seconds
Explanation:
Velocity and (constant) acceleration are related by ...
v = at
Filling in the numbers, we can solve for t:
18 m/s = (7 m/s²)·t
t = (18 m/s)/(7 m/s²) = (18/7) s = 2 4/7 s
It takes the cyclist 2 4/7 seconds (about 2.57 seconds) to reach 18 m/s.
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Comment on the subject
Problems involving position and its derivatives can reasonably be posted in the Math section. When energy or mass get involved, the Physics section is a better place. The relevant formulas for those are not always covered in algebra classes.